Performance of silver nanoparticle-impregnated ovoid ceramic water filters†
A ceramic water filter (CWF) with curved (ovoid) walls has been developed by Potters without Borders, a nonprofit that provides technical assistance to CWF factories. Here, a modified version of the USEPA testing method was used to evaluate the performance of ovoid CWFs, which have yet to be studied in the literature. Filters with/without silver nanoparticles (AgNPs) were evaluated for bacterial removal, turbidity removal, flow rate, and silver leaching. Log removal values (LRVs) for Escherichia coli for AgNP coated CWFs were 9.5–10.9 LRV while uncoated achieved 8.0–9.8 LRV. All the CWFs tested here had flow rates between 0.8 and 1.3 L h−1. The turbidity of the influent was reduced by the filters throughout the general and challenge water conditions with removal of 9.1–90.9% and 99.3–99.8%, respectively. Silver-coated CWFs had a higher total effluent silver concentration compared to uncoated (coated CWFs had 74% more total silver leaching on average) and had an increased silver release during the challenge phase (35 ppb) compared to the general phase (13 ppb). The exterior wall coated with AgNPs was shown to leach silver off the ceramic using X-ray photoelectron spectroscopy, providing evidence that supports the recommendation to coat only the interior wall of CWFs with AgNPs. The procedure demonstrated utility as a reproducible performance testing technique. X-ray diffraction and mercury intrusion porosimetry were used to study the ceramic structure.